Arrange the following steps of Polymerase Chain Reaction in correct sequence.
(A) Amplified DNA fragments
(B) Annealing of primers
(C) Extension
(D) Denaturation of dsDNA
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → (D), (B), (C), (A)
Each cycle is denaturation (D), annealing (B) and extension (C); repeating it gives amplified DNA (A).
Note: A similar question was also asked in CUET (UG) 2025 on 02-06-2025 (Slot 2), and in CUET (UG) 2023 on 15-06-2023 (Slot 1), on 12-06-2023 (Slot 2), on 07-06-2023 (Slot 3) and on 31-05-2023 (Slot 3).
NCERT Extract:
Amplification of Gene of Interest Using PCR – “PCR stands for Polymerase Chain Reaction. In this reaction, multiple copies of the gene (or DNA) of interest is synthesised in vitro using two sets of primers (small chemically synthesised oligonucleotides that are complementary to the regions of DNA) and the enzyme DNA polymerase. The enzyme extends the primers using the nucleotides provided in the reaction and the genomic DNA as template. If the process of replication of DNA is repeated many times, the segment of DNA can be amplified to approximately billion times, i.e., 1 billion copies are made. Such repeated amplification is achieved by the use of a thermostable DNA polymerase (isolated from a bacterium, Thermus aquaticus), which remain active during the high temperature induced denaturation of double stranded DNA.”